Grain oriented electrical steel sheets, which are mainly used as iron cores of transformers, are required to have excellent magnetic properties, in particular, less iron loss.
To meet this requirement, it is important that secondary recrystallized grains are highly aligned in the steel sheet in the (110)[001] orientation (or so-called “Goss orientation”) and impurities in the product steel sheet are reduced. However, there are limitations to control crystal orientation and reduce impurities in terms of balancing with manufacturing cost, and so on. Therefore, techniques have been developed to introduce non-uniform strain to the surfaces of a steel sheet in a physical manner and reducing the magnetic domain width for less iron loss, namely, magnetic domain refining techniques.
For example, JP 57-002252 B proposes a technique for reducing iron loss of a steel sheet by irradiating a final product steel sheet with a laser, introducing a high dislocation density region to the surface layer of the steel sheet and reducing the magnetic domain width.
In addition, JP 62-053579 B proposes a technique for refining magnetic domains by forming grooves having a depth of more than 5 μm on the base iron portion of a steel sheet after final annealing at a load of 882 to 2156 MPa (90 to 220 kgf/mm2), and then subjecting the steel sheet to heat treatment at a temperature of 750° C. or higher.
With the development of the above-described magnetic domain refining techniques, grain oriented electrical steel sheets having good iron loss properties may be obtained.
However, among the above-mentioned techniques for performing magnetic domain refining treatment by forming grooves, particularly, techniques for forming linear grooves by electrolytic etching for magnetic domain refining treatment do not always offer a sufficient effect on reducing iron loss as compared to other magnetic domain refining techniques for introducing high dislocation density regions by laser irradiation, and so on.
It could therefore be helpful to provide a grain oriented electrical steel sheet with an improved iron loss reduction effect when linear grooves for magnetic domain refinement are formed by electrolytic etching, and an advantageous method for manufacturing the same.